1. Technical Field
The present invention relates to a nickel-zinc-copper (NiZnCu) based ferrite composition, and a multilayered chip device using the same.
2. Description of the Related Art
Generally, as a magnetic material for a magnetic ceramic component such as a multilayered chip power inductor, or the like, nickel-zinc (NiZn) ferrite, nickel-zinc-copper (NiZnCu) ferrite, or the like, has been mainly used.
Among them, in order to further increase sinterability in the NiZn ferrite, a ternary composition of NiZnCu ferrite obtained by adding Cu to the NiZn ferrite has been mainly used. Meanwhile, in NiZnCu ferrite, Fe may be substituted with other metal ions. Further, in NiZnCu ferrite, Ni, Zn, or Cu may be substituted with other metal ions. That is, Ni, Zn, or Cu is substituted with an element having a similar ionic radius and an element having the same ionic valency to improve characteristics.
Among the above mentioned ferrite materials, the NiZnCu ferrite has been generally used for a multilayered chip inductor, a multilayered chip bead, a multilayered power inductor, or the like. Contents of NiO, ZnO, CuO, and Fe2O3 configuring the NiZnCu ferrite are changed to change permittivity, quality factor (Q), density, and magnetic characteristics of the NiZnCu ferrite, thereby implementing desired characteristics.
Meanwhile, multilayered chip devices such as a multilayered chip inductor, a multilayered chip bead, and a multilayered power inductor are manufactured using this ferrite composition. In the chip device, an internal electrode is made of silver (Ag).
Since Ag used as a material of the internal electrode has a melting point of 961° C., a ferrite composition fired at a temperature of 961° C. or less is required in order to implement a chip device. When a firing temperature is 900° C., it is preferable that a sintered density is at least about 4.8 g/cm3 or more.
Further, the multilayered power inductor has been used for a direct current (DC)-DC converter. Generally, it is advantageous that a quality factor (Q) is high. The high the quality factor (Q), the more preferable. The reason is that when a large Q means low loss. The quality factor (Q) may be represented by Q=2π fL/Rs, where f means a frequency, L means an inductance value, and Rs means an equivalent series resistance (ESR). As Rs is decreased, efficiency of the DC-DC converter is increased. Therefore, the above equation may be rearranged as follows: Rs=2π fL/Q. Here, when Q is large, Rs becomes small. It is very important factor in a chip device to increase Q.